Planar waveguide lasers have a structure in which the upper and lower surfaces of a thin planar laser medium extending in the oscillation direction of laser light are sandwiched between cladding layers having a lower refractive index than that of the laser medium, and in which the laser medium serves as a waveguide. Such a planar waveguide laser has a thin waveguide and a high excitation density. Accordingly, even in a case where a laser medium with a small stimulated-emission cross-section is used, a large gain can be achieved, and a highly-efficient oscillation operation can be performed. Furthermore, by widening the waveguide in the width direction, the output can be scaled while the excitation density is maintained at a predetermined value.
A conventional planar waveguide laser device as disclosed in Patent Literature 1 has a waveguide that is formed with a laser medium and claddings joined to both faces of the laser medium. End facet(s) of this waveguide is coated with a dielectric multilayer film so as to have desired optical characteristics. Note that, for ease of explanation, the cladding joined to the upper surface of the laser medium will be hereinafter referred to as the upper cladding, and the cladding joined to the lower surface of the laser medium will be hereinafter referred to as the lower cladding.
In manufacturing planar waveguide laser devices, the upper and lower claddings having a lower refractive index than that of the laser medium are joined using a method such as vapor deposition or optical joining, or an optical adhesive, so that the upper cladding, the laser medium, and the lower cladding are integrated to form a waveguide. A portion to serve as an end facet of the integrated waveguide is optically polished, and then a coating is applied to the optically polished surface. Cutting is performed from a direction perpendicular to the waveguide surface, so that planar waveguide laser elements of a desired size are produced.